The primary application of this invention is in balancing a rotating shaft assembly, such as is found in multi-stage turbo generators, for example, but the invention has application to other machinery.
By way of illustration, in a steam turbine driven generating station, during the start up after initial assembly or after any reassembly, the train of drive shafts often requires balancing. During normal operation, erosion of the blading, unsymmetrical coating of the blading or distortion of various components of the turbines makes it necessary to rebalance the assembly. Presently, the machinery is shut down, and a balance weight added which is usually conservatively calculated to reduce the vibrations at the point along the shaft having the highest vibrations without increasing the vibrations at other axial locations significantly. However, due to the non-linear stiffness characteristics inherent in fluid film bearings, which are commonly used in most of this machinery, the relationship between angular location of the peak vibration and the angular location of a corrective balance weight is not precisely known, and the relationship between the vibration amplitude and the magnitude of the corrective weight is not precisely known. Thus, in most applications of multi-bearing trains of rotating machinery, there is substantial risk that a balance weight may not reduce the vibrations as expected, even with the most sophisticated vibration data gathering instrumentation and balance weight calculation programs presently available. This is due to the extreme complexity of the mechanical structure of the rotating trains, and has very little to do with the vibration data gathering systems or the balance weight calculation procedures. The present way to balance these units is to start up the unit, measure and record the vibration data at all speeds and loads considered significant, load up the unit, shut down the unit, calculate a new balance weight or set of balance weights, install the weights with the machine stopped, restart the unit, measure the vibrations, and repeat the process until the vibrations are considered satisfactory. It can be appreciated that starting up and shutting down a major generator is a costly and complicated process. The desirability of balancing a rotating member while it is rotating has long been recognized. The art as applied to grinding wheels is well developed. However, the apparatus for accomplishing the balancing of grinding wheels has been very complicated, and has been predicated on the fact that the balancing apparatus can be either mounted on the wheel itself or on a stub shaft, generally made hollow to receive a control rod in which, because it extends through and along the axis of rotation, can either be moved axially or held against rotation to actuate a balancing mechanism. U.S. Pat. Nos. illustrating this approach include: Lehman, 4,474,076, Kida et al., 3,918,326, Dahlin, 4,041,802, Kurkowski et al 3,952,612, Kimmelaar 3,866,489, Liebmann et al., 3,827,193, Vetter, 3,822,514, Ito, 3,698,263, Held, 3,376,759, and Achilles, 3,177,738.
The teachings of this art are not applicable to the balancing of a drive train that extends uninterruptedly between successive pieces of equipment, and, as has been indicated, no balancing apparatus capable of operation while the shafts are rotating has been put into commercial operation in power plants and pumping stations and the like, to the knowledge of the applicants.
One of the objects of this invention is to provide an actuating mechanism that can be installed on a shaft intermediate its ends without access to one end, and be operated, without access to an end of the shaft, while the shaft is rotating.
Another object is to provide such a device that is simple, highly dependable and rugged, and which permits fine adjustment.
Other objects will become apparent to those skilled in the ar in the light of the following description and accompanying drawings.